The present invention relates to clean electric power generation in which toxins in flue gas emissions are minimized for a given power output.
It is well known in older electric power plants to burn solid carbonaceous material in the presence of an oxygen-containing gas in a combustion chamber to produce heat which creates steam that is fed to a turbine where it is expanded to produce electricity. The combustion of carbonaceous materials, such as coal, in the production of electricity can cause undesirable air pollution problems because the flue gases may contain toxic heavy metals, such as mercury, along with other undesirable byproducts such as SOx, CO and NOx. To maintain, or improve, air quality, it is important to minimize the production of these undesirable compounds.
Since it is very expensive to remove undesirable compounds from the flue gases of electric power plants, it has been proposed to remove the compounds from the carbonaceous materials prior to combustion.
Fuel gasification provides one known solution for removing undesirable compounds from solid carbonaceous materials. In a conventional coal gasification unit, typically used in a synthetic fuel plant, solid carbonaceous material, or coal, reacts with oxygen to produce a synthetic gas, commonly known as syngas.
One problem with utilizing syngas to generate power is that it is generally not economical to transport syngas over long distances. This has led to proposals for integrated gasification and electric power generation plants where the syngas is converted to electricity on-site.
One known integrated process which attempts to enhance power plant efficiency is described in U.S. Pat. No. 3,986,349 to Egan. In Egan, solid carbonaceous material is first gasified to produce syngas. A portion of this syngas is then contacted with Fischer-Tropsch and hydrogenation catalyst s to produce liquid hydrocarbons. The hydrocarbons are utilized as a fuel for a gas turbine to produce supplemental power for peak load demand. Egan further teaches that a portion of the unreacted syngas can be utilized to generate a base-load power output.
Although such an integrated process may help solve the problem of syngas transportation and clean fuel preparation, it is not economical to build an on-site gasification process simply to remove undesirable compounds upstream of combustion because of the large capital and operational expenses involved.
It is an object of this invention to maintain or lower the undesirable components of exhaust gas emissions of an electric power plant by fueling the electric power plant with clean unreacted syngas discharged from a coal gasification unit of an adjacent syngas plant.
According to the inventive method, electricity is generated from fuel provided by a syngas plant in proximity with an existing electric power plant and by carbonaceous material. The power plant operates within predetermined environmental limits on exhaust gas emissions. The syngas plant is used to produce liquid fuel and unreacted syngas in a Fischer-Tropsch reactor. The unreacted syngas is conducted to the power plant combustion chamber for use as a clean fuel moiety of the carbonaceous material burned in the combustion chamber. The unreacted syngas enables the electric power plant to operate below environmental limits in producing steam to generate electricity.